This invention is directed generally to the area of passive inflatable restraints or airbags for automotive vehicle occupants, and more particularly to an improved packaging of application specific integrated circuits for controlling deployment of such airbags, as well as a novel initiator design which incorporates an application specific integrated circuit.
An airbag restraint system is often provided in the form of a module including a housing which encloses a gas generator or inflator and at least part of an airbag, and a cover which conceals the module from view. The cover may be incorporated into the interior design of the vehicle in which the airbag restraint system or module is to be employed. Previously, such modules were employed on the driver side and on the passenger side at the front of the vehicle for protecting driver and passenger from front end collisions. The driver side module is often incorporated in the steering wheel of the vehicle while the passenger side module is often incorporated in the dashboard, aligned with the front passenger seating area.
More recently, airbag modules have also been employed to protect against side impact. These side modules are often incorporated in the vehicle doors on both the driver and passenger sides of the vehicle. More recently yet, there has been discussion of employing airbag modules at yet other parts of the interior of the vehicle to protect against various other types of impact at different points of the vehicle.
Typically, the inflator produces an inert gas such as nitrogen, which is directed into the airbag to force the airbag into the passenger compartment of the vehicle. In a pyrotechnic type of inflator, this gas is produced by the burning of a gas generating material. In order to trigger or initiate the burning of the gas generating material in such a pyrotechnic inflator an initiator or so-called squib is generally utilized. A typical initiator has a bridge wire embedded in a pyrotechnic material that will ignite or fire rapidly when brought to sufficiently high temperature. Heating of the bridge to a required temperature is normally effected by passing a direct electrical current through the bridge. The amount of electrical current required to obtain the firing temperature is generally relatively small.
Other types of inflator modules are also utilized which produce inflating gas by the rapid release of a quantity of gas stored under pressure. Still other so-called "hybrid" inflators utilize both a quantity of gas stored under pressure as well as a quantity of gas produced by the burning of a pyrotechnic material. However, most designs for these two types of inflators also employ an initiator device of the general type described above for triggering the production and/or release of gas by the inflator.
In order to control the timing and circumstances under which the required direct current is provided to the bridge wire of the initiator, suitable electronic control circuitry is usually employed. This control circuitry incorporates diagnostics and deployment circuitry often referred to as a sensing and diagnostic module (SDM) and also known as an electronic control unit (ECU). This SDM or ECU provides a number of functions including testing and confirming the state of the initiator in both "ready" and "fired" modes, sensing the occurrence of an event requiring deployment of one or more airbags, arming the initiator and inhibiting or enabling the firing of the initiator, as well as applying energy required to fire the initiator. The ECU may also include a control and processing circuit which may interface with similar circuits associated with other inflator modules in the vehicle or with a host computer.
Often, the ECU (or SDM) has been mounted on one or more circuit boards located at various places in the vehicle. However, in the case of multiple inflator modules in various areas of the vehicle, some or all of the functions of the ECU may be centralized to avoid duplicative circuitry for functions common to all of the inflator modules. Moreover, with multiple modules, a central control unit may be used to make various decisions, for example whether to deploy only a single airbag or multiple airbags, depending on the nature of an airbag deployable event which is sensed. However, with the utilization of only a single central circuit for performing some or all of the functions of the ECU, there is the attendant problem of additional wiring and routing of signals to multiple inflator modules in the vehicle.
Thus, in designing a vehicle with multiple airbags, a number of choices must be made, e.g. whether to centralize all of the control circuit functions, to employ a distributed design wherein the several control functions to be performed are assigned to different locations in the vehicle, or to employ duplicate electronic control units individually in each inflator module to be utilized in the vehicle. However, the last approach still leaves the question of providing for coordination between the various modules in a deployment situation, which may require a communications bus to link the ECUs of several inflator modules.
The present invention proposes a novel design for an electronic control unit, employing application specific integrated circuits in a novel package or configuration. The present invention also proposes employing one or more application specific integrated circuits as a modular part of the initiator or squib element of an inflator for an airbag deployment system. By housing one or more application specific integrated circuits with the initiator, some or all of the functions of the ECU can be performed at the initiator. This approach can facilitate a number of different design choices in the placement of other parts of the ECU circuitry at other locations in the vehicle. This could also simplify the wiring as compared to using a central ECU connected to multiple inflator modules. In the event all of the ECU functions were incorporated in application specific integrated circuits mounted in the initiator, theoretically only positive voltage and ground connections, and a communications bus for allowing communication between the ECUs at the different airbag locations would be required, greatly simplifying vehicle wiring with respect to the airbag deployment components.
In the past, the initiator has usually been constructed utilizing a glass and metal header which supports the bridge wire and a suitable electrical connector for joining the firing circuitry to the bridge wire. Typically, a plastic outer body of the initiator is injection molded around the glass and metal header. The heat and pressure involved in this injection molding process would probably destroy or seriously damage the electronic components of an application specific integrated circuit were the same to be employed as a part of the initiator.